Chunfei Wu

Published On November 26, 2022

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CO2 absorption - solvent - Ammonia-based - Techno-economic analysis - Model development and methodologies of TEA

Description of the Technical, Economic, and Environmental Indicators

https://doi.org/10.1016/j.seppur.2021.118959

2.3.1. Technical Indicators

Integrating the CO₂ capture process by chemical absorption in a steam power plant has a significant impact on its overall performance, decreasing the overall efficiency due to the necessary heat for the regeneration process and to cool the flue gases and chemical solvent. Thus, an analysis of the performance of the steam power plant before and after integrating the CO₂ capture process was conducted, based on the thermal and overall efficiency. Relationships (3)–(5) show the method of calculating the thermal efficiency, overall efficiency, and penalty efficiency after integrating the CO₂ capture process.

Thermal efficiency:

η t h e r m a l = L i n / q i n \cdot 100, [%]

(3)

where $L_{i n}$ is the internal mechanical work, in kJ/kg and $q_{i n}$ is the heat quantity, in kJ/kg.

Overall efficiency:

η o v e r a l l = η t h e r m a l \cdot η m e c h a n i c \cdot η g e n e r a t o r \cdot η b o l i e r \cdot 100, [%]

(4)

where $η_{m e c h a n i c}$ is the mechanical efficiency; $η_{g e n e r a t o r}$ is the generator efficiency; and $η_{b o i l e r}$ is the boiler efficiency.

Overall efficiency of penalties:

P e f = η o v e r a l l _ w i t h o u t _ C A P - η o v e r a l l _ w i t h _ C A P η o v e r a l l _ w i t h o u t _ C O 2 _ c a p t u r e \cdot 100, [%]

(5)

where $η_{o v e r a l l_w i t h o u t_C A P}$ is the overall efficiency of steam power plant without chemical absorption process and $η_{o v e r a l l_w i t h_C A P}$ is the overall efficiency of steam power plant with chemical absorption process.

2.3.2. Economic Indicators

As part of this analysis, the following economic and financial indicators were calculated:

Levelized cost of electricity—LCOE;
Capture cost per ton of CO₂;
Net present value—NPV;
Internal rate of return—IRR;
Discounted payback period—DPP; and
Profitability index—PI.

The LCOE was determined as the sum of investment costs, maintenance costs, and operating costs, relative to the electricity produced and taking into account the devaluation of money in time through the discounted rate considered (Relation (6)). The variable costs of maintenance and operation, respectively, of thermal power plants fitted with capture technology, do not include the CO₂ transport and storage costs [33].

L C O E \sum l y = 1 ( I + C 0 + C m + C d ) \cdot ( 1 + r ) - l \sum l y = 1 E e l \cdot ( 1 + r ) - l = ( I + l \cdot C 0 + l \cdot C m ) \cdot ( 1 + r ) - l l \cdot E e l \cdot ( 1 + r ) - l, [€ / MWh]

(6)

where $L C O E$ is the levelized cost of electricity, in €/MWh; I is the initial investment in the steam power plant plus the CO₂ capture technology investment cost, in €; $C_{0}$ is the operating costs, in €; $C_{m}$ is the maintenance costs, in €; $C_{d}$ is the dismantling costs, in €, in this analysis, these costs were considered as 0; r is the discount rate, considered r = 8% (for the energy sector, the discount rate was chosen between 8–12%); and $y$ is the lifetime of the steam power plant, in years, $(y \in 1 \dots l)$ . In this study, l was envisioned for 30 years, starting to generate electricity after three years, in the first three years after the investment has been made; and $E_{e l}$ represents the electricity produced in MWh.

To determine the costs associated with the integration of the CO₂ capture unit into the steam power plant, the CO₂ capture cost ( $C o s t_C O_{2_c a p t u r e d}$ , in €/kgCO₂) was calculated with Relation (7) [33]:

C o s t_C O 2_c a p t u r e d = L C O E w i t h _ C A P - L C O E w i t h o u t _ C A P C O 2 _ c a p t u r e d, [€ / t]

(7)

where $L C O E_{w i t h_C A P}$ / $L C O E_{w i t h o u t_C A P}$ is the discounted cost of electricity with and without capture technology, in €/MWh; $C O_{2_c a p t u r e d}$ is the amount of CO₂ captured, in relation to electricity production (emission factor), in kg/MWh; and $C O_{2_w i t h o u t_C A P}$ / $C O_{2_w i t h_C A P}$ is the amount of CO₂ emitted without/with collection technology linked to electricity production, in kg/MWh.

The CO₂ emissions tax is an indicator that measures the cost avoided thanks to CO₂ emissions generated in the environment compared to steam power plants without CO₂ capture technology. The CO₂ emissions tax is calculated according to the tax per ton of CO₂ $(T_{C O_{2}})$ and the quantity of CO₂ produced from the combustion of the fuel ( $M_{C O_{2}}$ ) (Relation (8)). The integration of CO₂ capture technology into the steam plant will therefore reduce CO₂ emissions considerably and thus increase the cost of electricity produced.

C C O 2 = M C O 2 \cdot T C O 2, [€ / an]

(8)

The NPV indicator is calculated as the sum of the annual discounted net income. This indicator is strongly influenced by the delay in updating the net result. In Relation (9), the determination of NPV is shown [34]:

N P V = \sum y = 1 l f I N y - C y - A y ( 1 + r ) i - \sum y = 1 l p i I y \cdot (1 + r) y, [€]

(9)

where $I N_{y}$ is the income for year y, in €/year; $C_{y}$ is the operating and maintenance costs for year y, with taxes and duties, but without depreciation, in €/year; $A_{y}$ is the annuity for year y, in the event of a loan, in €/year; $I_{y}$ is the equity investment made for year y, in €/year; r is the discount rate for the energy sector between 8 and 12%; l_f is the functional life of the steam power plant, in years; and $l_{p i}$ is the initial investment period, in years. For the second amount, if the investment made is not the same each year, the time axis must be taken into account (the time axis of the investment has the opposite meaning to the time axis of the investment project).

An investment project is economical if

N P V \geq 0

. If we compare several cases of the investment project, the optimal case is the one for which

N P V = m a x

The IRR is equal to the discount rate for which the NPV is 0 (Relation (10)) [34].

N P V = \sum y = 1 l I N y - C y - I y ( 1 + I R R ) y = 0, [€]

(10)

The IRR can have the following economic interpretations, if it has a single value: (1) IRR represents the percentage of interest, in the case of investments, of working capital, for which the project does not generate losses; and (2) IRR is the highest rate of annual profit that the investment project is expected to generate.

The DPP (Relation (11)) is the duration after the initial investment is paid back [34].

D P P = \sum y = 1 D P P I N y - C y - I y ( 1 + r ) y, [€]

(11)

For an investment project to be profitable in terms of return on investment, it is compared to its lifespan. Therefore, in the case of DPP, it must be less than the service life.

Relation (12) presents the determination of PI [34].

P I = N P V D I = D I N - D C D I = N P V + D I D I

(12)

where $N P V$ is the discounted income, the difference between the discounted revenue, and discounted expenditure; $D I$ is the updated investment; $D I N$ is the discounted income; and $D C$ is the discounted expenditure.

An investment project is economically efficient if

P I \geq 1

; if

P I < 1

, the project becomes economically inefficient.

2.3.3. Environmental Indicators

The LCA method was applied to calculate the environmental indicators. The LCA method consists of four stages according to ISO 14040: goal and scope definition, inventory analysis, impact assessment, and interpretation [35].

According to this methodology, the first step is to clearly identify the field of study for the systems studied. We also identified all the input and output flows of the processes that take place in the field of study [36,37,38,39].

The data collected and the results for the analyzed steam power plants are related to the functional unit (FU). In this article, the functional unit is given by 1 MWh produced by the steam power plant.

To simplify the analysis carried out in this study, the fuel life cycle is composed of two stages: extraction, treatment, and transport processes are part of the first stage, while the fuel combustion process is part of a second stage. This analysis did not consider the manufacture of equipment used in the two stages or their dismantling during the life cycle. The electricity consumed during the stages of the life cycle was also considered to come from the national energy sector.

The steam power plant was analyzed with and without CO₂ capture by the chemical absorption process. The CO₂ compression, transport, and storage steps were considered in this analysis.

The quantified impact indicators are abiotic depletion potential—ADP, global warming potential—GWP, eutrophication potential—EP, acidification potential—AP, photochemical ozone creation potential—POCP, and human toxicity potential—HTP. Table 4 presents the pollutants that contribute to each impact class, their contributions, and their specific relationship.

The impact indicators were determined from the emissions identified in the inventory analysis. Equation (13) was used to quantify the impact classes [40].

E = \sum k E k \cdot m k, [kg_eq / F . U .]

(13)

where $E_{k}$ is the impact of pollutant k on indicator E, in kg_eq/kg; and $m_{k}$ is the amount of pollutant produced, in kg/FU. For the ADP, $m_{r}$ is the mass of fuel (coal), in kg/FU and $E_{r}$ is the impact of coal on the ADP indicator, in kg_eq/kg (Table 5).

Table 5. Classification and quantification of emissions [41].

Impact Evaluation	Pollutants	Equation Used	Values
ADP [kg_Sb_eq/FU]	–	$A D P = \sum_{r} A D P_{r} \times m_{r}$ $A D P_{r}$ —ADP for each resource “r”, [kg_Sb_eq/kg] $m_{r}$ —quantity used for the resource “r”, [kg/FU]	ADP_{natural gas} = 0.0187 ADP_{hard coal} = 0.0134 ADP_lignite = 0.00678
GWP [t_CO₂_eq/FU]	CO₂, CH₄, N₂O	$G W P = \sum_{k} G W P_{k} \times m_{k}$ $G W P_{k}$ – GWP for each pollutant “k”, [kg_CO₂_eq/kg] $m_{k}$ —quantity used for the pollutant “k”, [kg/FU]	GWP_CO2 = 1 GWP_CH4 = 21 GWP_N2O = 310
AP [t_SO₂_eq/FU]	SO₂, NH₃, NO₂	$A P = \sum_{k} A P_{k} \times m_{k}$ $A P_{k}$ —AP potential for each pollutant “k”, [kg_SO₂_eq/kg] $m_{k}$ —quantity used for the pollutant “k”, [kg/FU]	AP_SO2 = 1.2 AP_NH3 = 1.6 AP_NO2 = 0.5
POCP [t_C₂H₄_eq/FU]	CO, SO₂, CH₄, CH₂O, NO₂	$P O C P = \sum_{k} P O C P_{k} \times m_{k}$ $P O C P_{k}$ —POCP potential for each pollutant “k”, [kg_C₂H₄_eq/kg] $m_{k}$ —quantity used for pollutant “k”, [kg/FU]	POCP_CO = 0.027 POCP_SO2 = 0.048 POCP_CH4 = 0.006 POCP_CH2O = 0.519 POCP_NO2 = 0.028
EP [t_PO₄³⁻_eq/FU]	NO, NH₃, NO₂, COD, NH₄	$E P = \sum_{k} E P_{k} \times m_{k}$ $E P_{k}$ —EP potential for each pollutant “k”, [kg_PO₄³⁻_eq/kg] $m_{k}$ —quantity used for the pollutant “k”, [kg/FU]	EP_NO = 0.2 EP_NH3 = 0.35 EP_NO2 = 0.13 EP_COD = 0.022 EP_NH4 = 0.35
HTP [t_1.4DCB_eq/FU]	SO₂, NH₃, NO₂, Dust, CH₂O, Pb, Phenol, HCl, HF	$H T P = \sum_{k} \sum_{c o m} H T P_{c o m, k} \times m_{c o m, k}$ com: compartment (air, water soil); $H T P_{c o m, k}$ —HTP potential for each pollutant “k”, and for each compartment, [kg_1.4DCB_eq/kg] $m_{c o m, k}$ —quantity used for the pollutant “k” and compartment, [kg/FU]	HTP_SO2 = 0.096 HTP_NH3 = 0.1 HTP_NO2 = 1.2 HTP_Dust = 0.82 HTP_CH2O = 0.83 HTP_Pb = 3300 HTP_Phenol = 0.52 HTP_HCl = 0.5 HTP_HF = 94

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Chunfei Wu

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Description of the Technical, Economic, and Environmental Indicators

2.3.1. Technical Indicators

2.3.2. Economic Indicators

2.3.3. Environmental Indicators

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